1. Field of the Invention
The present invention relates to the packaging industry, more specifically for packaging sticks of substances of the lipstick type in cases having a rotary lifting mechanism which makes it possible to move the stick out of the case at the time of use without separating it from the case, then to withdraw it into the case until the next time it is used.
2. Description of the Prior Art
A conventional case has a stick-holder cup which is capable of sliding axially within two mutually rotating concentric coaxial sleeves, namely a stationary outer sleeve and a rotary inner sleeve. In the outer sleeve are cut two internal helical grooves symmetrically displaced by 180.degree.. The rotary inner sleeve has two diametrically opposite and symmetrical longitudinal slots, each slot being branched-off at 90.degree. into a recess at each end of travel of the cup. The recess is oriented in the direction opposite to the rotation of the sleeve which brings the cup to this end of its travel. The cup has two radial nipples relatively displaced by 180.degree., and each nipple passes respectively through a slot so as to penetrate into a groove at its distal end.
For reasons of appearance and cost, it is standard practice to construct the mechanisms of these cases from thin materials which usually consist of plastics. The mechanical strength of plastics proves suitable for normal use, but may sometimes be insufficient to prevent the nipples from escaping from the channels and the slots when an excessive twist is exerted at the end of travel of the cup. The accidental disengagement thus produced has an adverse effect on the subsequent operation of the mechanism. In order to overcome this drawback, the thickness of the wall inner and of the outer sleeves is increased to the maximum extent which is compatible with a commercially acceptable diameter of the case, while endeavoring to find a compromise with attractiveness of appearance and cost. The compromise cannot be fully satisfactory.
The object of the invention is to overcome this disadvantage of conventional cases and to prevent accidental disengagement of the rotary mechanisms even with thin-walled sleeves.